Control apparatus for vehicle

ABSTRACT

In a vehicle incorporating an internal combustion engine having in-cylinder injectors and intake manifold injectors and performing engine intermittent operation control, at the end of vehicle operation, the fuel pressure is decreased in both a high-pressure delivery pipe and a low-pressure delivery pipe by actuation (opening) of an electromagnetic relief valve and by stop of operation of a low-pressure fuel pump. This prevents deterioration in emission performance at the next engine start attributable to fuel leakage due to degradation in oil tightness of the injectors during the operation stop period. When the engine is temporarily stopped by engine intermittent operation control, while the low-pressure fuel pump is stopped, actuation (opening) of the electromagnetic relief valve is prohibited. At the engine restart after temporary stop, the fuel in the high-pressure delivery pipe having its pressure secured at a certain level is injected to quickly start the engine.

This nonprovisional application is based on Japanese Patent ApplicationNo. 2005-078389 filed with the Japan Patent Office on Mar. 18, 2005, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control apparatus for a vehicle, andmore particularly to a control apparatus for a vehicle mounted with aninternal combustion engine having a first fuel injection mechanism(in-cylinder injector) for injecting fuel into a cylinder and a secondfuel injection mechanism (intake manifold injector) for injecting fuelinto an intake manifold and/or an intake port.

2. Description of the Background Art

A fuel injection apparatus provided with an in-cylinder injector forinjecting fuel into a cylinder and an intake manifold injector forinjecting fuel into an intake port, and controlling the in-cylinderinjector and the intake manifold injector in accordance with anoperation state to inject the fuel by combination of intake manifoldinjection and in-cylinder direct injection is known (e.g., JapanesePatent Laying-Open No. 07-103048, which is also referred to as “PatentDocument 1” hereinafter).

In a fuel supply system for supplying the fuel at a prescribed fuelpressure to the injectors, generally, one fuel line extending from afuel tank toward the internal combustion engine is branched in thevicinity of the internal combustion engine so as to supply the fuel tothe intake manifold injector and to the in-cylinder injector. With thisconfiguration, however, the fuel line has a complicated configuration inthe vicinity of the internal combustion engine, and the fuel suppliedfrom the fuel tank may be subjected to a great amount of heat from theengine block of the internal combustion engine. The fuel supplied to theintake manifold injector is a fuel of a low pressure that is pumped upfrom the fuel tank by using a low-pressure fuel pump. As such, it hasbeen pointed out that the fuel, when subjected to the great amount ofheat from the engine block, may partially vaporize in the fuel line or adelivery pipe for supplying the fuel into the intake manifold injector,leading to occurrence of vapor lock.

To address such a problem, for example, Japanese Patent Laying-Open No.2004-278347 (hereinafter, also referred to as “Patent Document 2”)discloses a fuel supply system in which a fuel tank, a low-pressure fuelpump, a fuel pressure regulator (pressure regulator), an intake manifoldinjection (low-pressure) delivery pipe, a high-pressure fuel pump, anin-cylinder injection (high-pressure) delivery pipe, and a relief valveare arranged in series. In a fuel injection apparatus provided with sucha fuel supply system, it is possible to prevent fuel injection failureattributable to the vapor lock caused in the pipe connected to theintake manifold injector, with a simple configuration.

In the fuel injection apparatus disclosed in Patent Document 2, theintake manifold injection (low-pressure) delivery pipe is arrangeddownstream of the fuel pressure regulator. Thus, although anelectromagnetic relief valve for releasing pressure is arrangeddownstream of the in-cylinder injection (high-pressure) delivery pipe,it is difficult to intentionally release the fuel pressure of thelow-pressure delivery pipe at the time of stop of operation of thevehicle. This leads to poor oil tightness, and there may occur leakageof the fuel from the intake manifold fuel injection valve during stop ofoperation of the vehicle. Such leakage of the fuel may lead todeterioration in emission performance at the time of next start of theengine.

In a hybrid vehicle further provided with an electric motor as anothersource of driving force other than the internal combustion engine, or ina vehicle mounted with a so-called economy running system that forciblystops idling of the engine at the time of temporary stop of the vehicle(hereinafter, also simply called the “eco run vehicle”), “engineintermittent operation control” is carried out in which an engine istemporarily stopped when a prescribed engine stop condition issatisfied, and restarted in response to fulfillment of an engine stopreset condition.

In the vehicle conducting such engine intermittent operation control,there are two cases of engine stop: one is stop associated with end ofvehicle operation, and the other is temporary stop with an assumption ofrestart of the engine. While it is necessary to secure quick startingcapability upon restart of the engine in the case of temporary stop ofthe engine according to the engine intermittent operation control, atthe time of engine stop associated with the end of vehicle operation, itis necessary to prevent deterioration in emission performance upon nextstart of vehicle operation attributable to degradation in oil tightness.

Further, there are also two cases of engine start: one is initial startassociated with start of vehicle operation, and the other is restartfollowing temporary stop in the engine intermittent operation. It ispreferable to set optimal engine starting conditions for the respectivecases for the purposes of securing starting capability of the engine aswell as preventing deterioration in emission performance.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is toprovide a control apparatus for a vehicle incorporating an internalcombustion engine having a first fuel injection mechanism (in-cylinderinjector) for injecting fuel into a cylinder and a second fuel injectionmechanism (intake manifold injector) for injecting fuel into an intakemanifold and/or an intake port and performing engine intermittentoperation control, that ensures smooth starting performance and alsoprevents deterioration in emission performance at the time of enginestart.

Another object of the present invention is to provide a controlapparatus for a vehicle incorporating an internal combustion enginehaving an in-cylinder injector and an intake manifold injector and alsoincorporating another driving force source other than the internalcombustion engine, that ensures smooth starting performance and alsoprevents deterioration in emission performance at the time of enginestart.

A control apparatus for a vehicle according to the present invention isfor a vehicle incorporating an internal combustion engine having a firstfuel supply system supplying fuel to a first fuel injection mechanismfor injecting fuel into a cylinder and a second fuel supply systemsupplying fuel to a second fuel injection mechanism for injecting fuelinto an intake manifold, and includes a fuel injection control portion,an intermittent operation control portion, and a first pressure releasecontrol portion. The fuel injection control portion controls a fuelinjection ratio between the first fuel injection mechanism and thesecond fuel injection mechanism with respect to a total fuel injectionquantity. The intermittent operation control portion automatically stopsthe internal combustion engine temporarily when a prescribed conditionis satisfied after start of operation of the vehicle. The first pressurerelease control portion controls a first pressure release mechanism thatis configured to guide the fuel in the first fuel supply system to apressure release path when actuated. The first pressure release controlportion prohibits actuation of the first pressure release mechanism whenthe internal combustion engine is in an automatically stopped state bythe intermittent operation control portion. The fuel injection controlportion includes a first startup-time injection control portionconfigured to set a ratio of a quantity of the fuel injected from thefirst fuel injection mechanism to the total fuel injection quantity near100% when the internal combustion engine is restarted from theautomatically stopped state.

According to the control apparatus for a vehicle described above, in thevehicle incorporating the internal combustion engine having the firstfuel injection mechanism (in-cylinder injector) and the second fuelinjection mechanism (intake manifold injector) and performing the engineintermittent operation control to automatically stop the internalcombustion engine temporarily after start of operation of the engine,the fuel of almost all of the total fuel injection quantity is injectedfrom the first fuel injection mechanism (in-cylinder injector) at thetime of engine restart after temporary stop of the engine by the engineintermittent operation control, by securing the fuel pressure of arequired level in the first fuel supply system for the in-cylinder fuelinjection, without actuating the first pressure release mechanism. Inthe engine intermittent operation after start of vehicle operation, thetemperature in the combustion chamber has been increased, and thecatalyst has also reached the active temperature. Thus, the in-cylinderfuel injection would not cause deterioration in emission performance.Accordingly, it is possible to quickly start the in-cylinder fuelinjection at the time of engine restart by the engine intermittentoperation control, to ensure starting capability of the vehicle withoutdeteriorating emission performance.

Preferably, the control apparatus for a vehicle of the present inventionfurther includes a second pressure release control portion. The secondpressure release control portion controls a second pressure releasemechanism that is configured to release a fuel pressure of the secondfuel supply system when actuated. Further, the first and second pressurerelease control portions actuate the first and second pressure releasemechanisms, respectively, in response to stop of the internal combustionengine in association with end of operation of the vehicle.

According to the control apparatus for a vehicle described above, at theend of vehicle operation, the fuel pressure can be decreased byactuating the pressure release mechanisms in both of the first fuelsupply system and the second fuel supply system. This can preventoccurrence of fuel leakage due to degradation in oil tightness of thefirst and second fuel injection mechanisms (injectors) during the periodwhere the vehicle operation is stopped until next start of operation.Accordingly, deterioration in emission performance at the next start ofthe internal combustion engine can be prevented.

Still preferably, in the control apparatus for a vehicle of the presentinvention, the first pressure release control portion actuates the firstpressure release mechanism at the end of operation of the vehicle, aftera lapse of a prescribed time that is set to allow a decrease of atemperature of the fuel in the first fuel supply system to a prescribedlevel.

In the control apparatus for a vehicle described above, the fuelpressure is decreased at the end of vehicle operation only after thefuel temperature in the first fuel supply system supplying thehigh-pressure fuel is decreased to a prescribed level. As such, it ispossible to prevent vapor lock that would occur due to boiling underreduced pressure when the pressure is rapidly released while the fueltemperature is still high.

Preferably, the control apparatus for a vehicle according to the presentinvention further includes a fuel pump control portion, which isconfigured to control a fuel pump for securing a fuel pressure necessaryfor the second fuel supply system. The fuel pump control portion stopsoperation of the fuel pump each time when the internal combustion engineis automatically stopped by the intermittent operation control portionand when the internal combustion engine is stopped in association withend of operation of the vehicle.

According to the control apparatus for a vehicle described above, thefuel pump is stopped in association with the temporary stop of theinternal combustion engine by the intermittent operation control. Thiscan improve fuel efficiency.

Still preferably, in the control apparatus for a vehicle according tothe present invention, the fuel injection control portion includes asecond startup-time injection control portion. The second startup-timeinjection control portion sets a ratio of a quantity of the fuelinjected from the second fuel injection mechanism to the total fuelinjection quantity near 100% when the internal combustion engine isstarted in association with start of operation of the vehicle.

According to the control apparatus for a vehicle described above, thefuel of almost all of the total fuel injection quantity required isinjected from the second fuel injection mechanism (intake manifoldinjector) at the start of the internal combustion engine in associationwith start of vehicle operation. As such, at the time when thetemperature of the combustion chamber and the temperature of thecatalyst are both low, the engine is started by injecting fuel into theintake manifold and/or the intake port, rather than directly injectingthe fuel into the cylinder. Accordingly, the engine can be startedwithout causing the inconvenience such as deterioration in emissionperformance or deterioration in lubrication performance of the internalcombustion engine by performing in-cylinder fuel injection in the enginecold state.

Particularly, in the above-described configuration, the vehicle furtherincorporates a driving force source besides the internal combustionengine, and the control apparatus further includes a driving force ratiocontrol portion. The driving force ratio control portion controls aratio of driving force generated by the internal combustion engine andby the driving force source, in accordance with an operation state.Further, the driving force ratio control portion instructs the drivingforce source to generate driving force corresponding to the drivingforce required for the vehicle as a whole, when the internal combustionengine is started in association with start of operation of the vehicle,and when a fuel pressure in the second fuel supply system is lower thana required level.

According to the control apparatus for a vehicle described above, in theconfiguration where the vehicle is further provided with another drivingforce source (typically, an electric motor) in addition to the internalcombustion engine, the driving force required for the vehicle as a wholeis provided by using the other driving force source when the fuelpressure in the second fuel supply system supplying the fuel to thesecond fuel injection mechanism (intake manifold injector) has notreached a required pressure level in the engine cold state. Accordingly,it is possible to ensure quick starting capability of the vehiclewithout causing the inconvenience by performing in-cylinder fuelinjection in the engine cold state.

According to the control apparatus for a vehicle described above, at theengine start associated with start of vehicle operation, the internalcombustion engine is started with the fuel injected from the second fuelinjection mechanism (intake manifold injector), and in the case wherethe fuel pressure in the second fuel supply system supplying the fuel tothe second fuel injection mechanism has not reached a required pressurelevel, the driving force requested to the vehicle is addressed by usingthe driving force generated by the other driving force source. As aresult, it is possible to secure quick starting capability of thevehicle without causing the inconvenience by performing in-cylinder fuelinjection in the engine cold state.

A control apparatus for a vehicle according to another configuration ofthe present invention is for a vehicle incorporating an internalcombustion engine, which has a first fuel supply system supplying fuelto a first fuel injection mechanism for injecting fuel into a cylinderand a second fuel supply system supplying fuel to a second fuelinjection mechanism for injecting fuel into an intake manifold, and adriving force source other than the internal combustion engine, andincludes a driving force ratio control portion and a fuel injectioncontrol portion. The driving force ratio control portion controls aratio of driving force generated by the internal combustion engine andby the driving force source in accordance with an operation state. Thefuel injection control portion controls a fuel injection ratio betweenthe first fuel injection mechanism and the second fuel injectionmechanism with respect to a total fuel injection quantity in theinternal combustion engine. The fuel injection control portion includesa startup-time injection control portion, which sets a ratio of aquantity of the fuel injected from the second fuel injection mechanismto the total fuel injection quantity near 100% when the internalcombustion engine is started in association with start of operation ofthe vehicle. Further, the driving force ratio control portion instructsthe driving force source to generate driving force corresponding to thedriving force required for the vehicle as a whole, when a fuel pressurein the second fuel supply system is lower than a required level.

According to the control apparatus for a vehicle described above, at thestart of the internal combustion engine in association with start ofoperation of the vehicle that incorporates the internal combustionengine that can effect both in-cylinder fuel injection and intakemanifold fuel injection and another driving force source (typically, anelectric motor) other than the internal combustion engine, the internalcombustion engine is started with the fuel injected from the second fuelinjection mechanism (intake manifold injector). Further, when the fuelpressure in the second fuel supply system supplying the fuel to thesecond fuel injection mechanism has not reached a required level, thedriving force requested to the vehicle is addressed by the driving forcegenerated by the other driving force source. As a result, it is possibleto ensure quick starting capability of the vehicle without causing theinconvenience (typically, deterioration in emission performance) byperforming in-cylinder fuel injection in the engine cold state.

Preferably, the control apparatus for a vehicle according to the otherconfiguration of the present invention further includes a fuel pumpcontrol portion. The fuel pump control portion controls a fuel pump forsecuring a fuel pressure necessary for the second fuel supply system,and starts operation of the fuel pump before a start instruction of theinternal combustion engine is generated.

According to the control apparatus for a vehicle described above, theoperation of the fuel pump is started prior to issuance of aninstruction to start the internal combustion engine. Thus, particularlyupon engine start in the engine cold state in association with start ofvehicle operation, it is possible to secure the fuel pressure of arequired level for the fuel injected from the second fuel injectionmechanism (intake manifold injector) in an early stage, to allow quickstart of the engine.

Still preferably, the driving force source is an electric motor poweredby a secondary battery, and the vehicle further includes a chargecontrol portion configured to charge the secondary battery by powergenerated by regenerative braking of the electric motor and by powergenerated by driving force of the internal combustion engine.

According to the control apparatus for a vehicle described above, in thehybrid vehicle incorporating an electric motor as another driving forcesource in addition to the internal combustion engine, the internalcombustion engine can be started smoothly, without causing the problemsof deterioration in emission performance and others.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of an engine system that iscontrolled by a control apparatus according to an embodiment of thepresent invention.

FIG. 2 illustrates a configuration example of a fuel supply system shownin FIG. 1.

FIG. 3 is a flowchart illustrating engine intermittent operationcontrol.

FIG. 4 is a flowchart illustrating pressure release control in the fuelsupply system shown in FIG. 2 in the control apparatus according to theembodiment of the present invention.

FIGS. 5 and 6 are operational waveform diagrams illustrating operationsof the fuel supply system according to the pressure release controlshown in FIG. 4.

FIG. 7 is a flowchart illustrating engine startup-time control by thecontrol apparatus according to the embodiment of the present invention.

FIG. 8 is a block diagram showing a schematic configuration of a hybridvehicle.

FIG. 9 is a flowchart illustrating the engine startup-time control inthe hybrid vehicle shown in FIG. 8.

FIG. 10 illustrates another configuration example of the fuel supplysystem shown in FIG. 1.

FIGS. 11 and 12 are operational waveform diagrams illustratingoperations of the fuel supply system shown in FIG. 10.

FIGS. 13 and 14 illustrate a first example of DI ratio setting maps (inthe engine warm state and the engine cold state, respectively) in theengine system shown in FIG. 1.

FIGS. 15 and 16 illustrate a second example of the DI ratio setting maps(in the engine warm state and the engine cold state, respectively) inthe engine system shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described indetail with reference to the drawings. In the drawings, the same orcorresponding portions have the same reference characters allotted, anddetailed description thereof will not be repeated in principle.

FIG. 1 schematically shows a configuration of an engine system providedwith an internal combustion engine controlled by a control apparatus fora vehicle according to an embodiment of the present invention. Althoughan in-line 4-cylinder gasoline engine is shown in FIG. 1, application ofthe present invention is not restricted to the engine shown.

As shown in FIG. 1, the engine (internal combustion engine) 10 includesfour cylinders 112, which are connected via corresponding intakemanifolds 20 to a common surge tank 30. Surge tank 30 is connected viaan intake duct 40 to an air cleaner 50. In intake duct 40, an airflowmeter 42 and a throttle valve 70, which is driven by an electric motor60, are disposed. Throttle valve 70 has its degree of opening controlledbased on an output signal of an engine ECU (Electronic Control Unit)300, independently from an accelerator pedal 100. Cylinders 112 areconnected to a common exhaust manifold 80, which is in turn connected toa three-way catalytic converter 90.

For each cylinder 112, an in-cylinder injector 110 for injecting fuelinto the cylinder and an intake manifold injector 120 for injecting fuelinto an intake port and/or an intake manifold are provided.

Injectors 110, 120 are controlled based on output signals of engine ECU300. In-cylinder injectors 110 are connected to a common fuel deliverypipe (hereinafter, also referred to as “high-pressure delivery pipe”)130, and intake manifold injectors 120 are connected to a common fueldelivery pipe (hereinafter, also referred to as “low-pressure deliverypipe”) 160. Fuel supply to fuel delivery pipes 130, 160 is carried outby a fuel supply system 150, which will be described later in detail.

Engine ECU 300 is configured with a digital computer, which includes aROM (Read Only Memory) 320, a RAM (Random Access Memory) 330, a CPU(Central Processing Unit) 340, an input port 350, and an output port360, which are connected to each other via a bidirectional bus 310.

Airflow meter 42 generates an output voltage that is proportional to anintake air quantity, and the output voltage of airflow meter 42 is inputvia an A/D converter 370 to input port 350. A coolant temperature sensor380 is attached to engine 10, which generates an output voltageproportional to an engine coolant temperature. The output voltage ofcoolant temperature sensor 380 is input via an A/D converter 390 toinput port 350.

A fuel pressure sensor 400 is attached to high-pressure delivery pipe130, which generates an output voltage proportional to a fuel pressurein high-pressure delivery pipe 130. The output voltage of fuel pressuresensor 400 is input via an A/D converter 410 to input port 350. Anair-fuel ratio sensor 420 is attached to exhaust manifold 80 locatedupstream of three-way catalytic converter 90. Air-fuel ratio sensor 420generates an output voltage proportional to an oxygen concentration inthe exhaust gas, and the output voltage of air-fuel ratio sensor 420 isinput via an A/D converter 430 to input port 350.

Air-fuel ratio sensor 420 in the engine system of the present embodimentis a full-range air-fuel ratio sensor (linear air-fuel ratio sensor)that generates an output voltage proportional to an air-fuel ratio ofthe air-fuel mixture burned in engine 10. As air-fuel ratio sensor 420,an ° 2 sensor may be used which detects, in an on/off manner, whetherthe air-fuel ratio of the mixture burned in engine 10 is rich or leanwith respect to a theoretical air-fuel ratio.

Accelerator pedal 100 is connected to an accelerator press-down degreesensor 440 that generates an output voltage proportional to the degreeof press-down of accelerator pedal 100. The output voltage ofaccelerator press-down degree sensor 440 is input via an A/D converter450 to input port 350. An engine speed sensor 460 generating an outputpulse representing the engine speed is connected to input port 350. ROM320 of engine ECU 300 prestores, in the form of a map, values of fuelinjection quantity that are set corresponding to operation states basedon the engine load factor and the engine speed obtained by theabove-described accelerator press-down degree sensor 440 and enginespeed sensor 460, respectively, and the correction values based on theengine coolant temperature.

Engine ECU 300 generates various control signals for controlling theoverall operations of the engine system based on signals from therespective sensors by executing a prescribed program. The controlsignals are transmitted to the devices and circuits constituting theengine system via output port 360 and drive circuits 470.

FIG. 2 illustrates in detail the configuration of fuel supply system 150shown in FIG. 1.

In FIG. 2, the portions other than in-cylinder injectors 110,high-pressure delivery pipe 130, intake manifold injectors 120 andlow-pressure delivery pipe 160 correspond to the fuel supply system 150of FIG. 1.

The fuel stored in a fuel tank 200 is discharged at a prescribedpressure by a low-pressure fuel pump 180 of an electric motor-driventype. Low-pressure fuel pump 180 is controlled based on an output signalfrom an ECU 300#. Here, ECU 300# corresponds to a functional part ofengine ECU 300 of FIG. 1 that is related to control of the fuelinjection apparatus.

The discharge side of low-pressure fuel pump 180 is connected via a fuelfilter 190 and a fuel pipe 135 to a low-pressure delivery pipe 160 thatis formed as a tubular body provided with intake manifold injectors 120.That is, low-pressure delivery pipe 160 receives the fuel dischargedfrom low-pressure fuel pump 180 via fuel pipe 135 on the upstream side,and delivers the fuel to intake manifold injectors 120 so as to beinjected into the internal combustion engine.

The downstream side of low-pressure delivery pipe 160 is connected viafuel pressure regulator 170 to the intake side of a high-pressure fuelpump 155 of an engine-driven type. Fuel pressure regulator 170 isconfigured to guide the fuel on the downstream side of low-pressuredelivery pipe 160 to a fuel return pipe 220 when a pressure of therelevant fuel becomes higher than a preset pressure. As such, the fuelpressure in low-pressure delivery pipe 160 is maintained so as not toexceed the preset pressure.

The discharge side of high-pressure fuel pump 155 is connected to a fuelpipe 165 via a check valve 140 that allows the flow toward the fuel pipe165. Fuel pipe 165 is connected to a high-pressure delivery pipe 130that is formed as a tubular body provided with in-cylinder injectors110.

The discharge side of high-pressure fuel pump 155 is also connected tothe intake side of high-pressure fuel pump 155 via an electromagneticspill valve 156. As the degree of opening of electromagnetic spill valve156 decreases, the quantity of the fuel supplied from high-pressure fuelpump 155 to fuel pipe 165 increases. When electromagnetic spill valve156 is fully open, fuel supply from high-pressure pump 155 to fuel pipe165 is stopped. Electromagnetic spill valve 156 is controlled inresponse to an output signal of ECU 300#.

High-pressure delivery pipe 130 receives on its upstream side the fueldischarged from high-pressure fuel pump 155 via fuel pipe 165, anddelivers the fuel to in-cylinder injectors 110 so as to be injected intothe internal combustion engine. Further, an electromagnetic relief valve210 is provided on the downstream side of high-pressure delivery pipe130. Electromagnetic relief valve 210 is opened in response to a controlsignal from ECU 300#, and guides the fuel within high-pressure deliverypipe 130 to fuel return pipe 220.

As such, in the fuel injection system according to the presentembodiment, low-pressure delivery pipe 160 and high-pressure deliverypipe 130 are arranged in series, as in Patent Document 2 describedabove, and then low-pressure delivery pipe 160 is arranged upstream offuel pressure regulator 170.

Such a configuration makes it possible to decrease the fuel pressure inthe high-pressure fuel supply system including high-pressure deliverypipe 130, by actuation (opening) of electromagnetic relief valve 210.Further, the fuel pressure in the low-pressure fuel supply systemincluding low-pressure delivery pipe 160 is decreased by stop ofoperation of low-pressure fuel pump 180. In the fuel supply system shownin FIG. 2, the high-pressure fuel supply system including high-pressuredelivery pipe 130 corresponds to the “first fuel supply system” of thepresent invention, and the low-pressure fuel supply system includinglow-pressure delivery pipe 160 corresponds to the “second fuel supplysystem” of the present invention. Further, electromagnetic relief valve210 corresponds to the “first pressure release means”, and issuance ofthe stop instruction of low-pressure fuel pump 180 corresponds to the“second pressure release means” of the present invention. Low-pressurefuel pump 180 corresponds to the “fuel pump”, and the functional part ofECU 300# controlling operation of low-pressure fuel pump 180 correspondsto the “fuel pump control means” of the present invention.

In the vehicle according to the embodiment of the present invention, itis assumed that the engine intermittent operation control, common in aso-called economy running system or in a hybrid vehicle, is carried outwherein engine 10 is temporarily stopped every time a prescribed enginestop condition is satisfied and it is automatically restarted inresponse to fulfillment of a reset condition of the engine stopcondition.

An intermittent operation control unit 302# shown in FIG. 2 representsthe functional block of engine ECU 300 of FIG. 1 related to theintermittent operation control. Intermittent operation control unit 302#receives signals necessary for determination of fulfillment of an enginestop condition and an engine stop reset condition, and generates anautomatic stop (temporary stop) instruction and a restart instruction ofthe engine. Intermittent operation control unit 302# corresponds to the“intermittent operation control means” of the present invention.

FIG. 3 is a flowchart illustrating the engine intermittent operationcontrol carried out by intermittent operation control unit 302#.

Referring to FIG. 3, in step S100, intermittent operation control unit302# determines whether a prescribed, automatic engine stop condition issatisfied. If not (NO in step S100), the operation of the engine iscontinued, and the engine intermittent operation control routine isterminated. The above-described automatic engine stop condition issatisfied, e.g., when the state where the vehicle speed=0 and theaccelerator press-down degree=0 continues for a predetermined period oftime and three-way catalytic converter 90 has also been increased intemperature and thus activated.

If the automatic engine stop condition is satisfied (YES in step S100),intermittent operation control unit 302# issues a temporary stopinstruction to engine 10 (step S110), and also outputs a stopinstruction to low-pressure fuel pump 180 (step S120).

After the temporary stop of the engine, it is determined periodicallywhether an engine stop reset condition is satisfied (step S130). As longas the engine stop reset condition is not satisfied (NO in step S130),engine 10 and low-pressure fuel pump 180 remain temporarily stopped.

If the engine stop rest condition is satisfied (YES in step S130),intermittent operation control unit 302# issues a restart instruction tolow-pressure fuel pump 180 (step S140), and also issues a restartinstruction to engine 10 (step S150). The engine stop reset condition isfulfilled when the above-described automatic engine stop condition is nolonger met, typically when the accelerator pedal is pressed down andthus the accelerator press-down degree≠0.

As described above, in the internal combustion engine according to theembodiment of the present invention shown in FIGS. 1 and 2, stop ofengine 10 includes the following two cases: stop of the enginecorresponding to the end of vehicle operation by turning off of theignition key, and temporary stop of the engine assuming restart thereofby the engine intermittent operation control.

In the case of temporary stop of the engine according to theintermittent operation control, it is critical to quickly restart thefuel injection at the restart of the engine. On the other hand, in thecase of stop of the engine associated with the end of vehicle operation,it is important to prevent degradation in oil tightness of in-cylinderinjector 110 and intake manifold injector 120 during the period wherevehicle operation is stopped. Thus, in the embodiment of the presentinvention, pressure release control, as will be described below, iscarried out in the fuel supply system shown in FIG. 2.

Referring to FIG. 4, engine ECU 300 determines whether the engine isbeing stopped or not, by detecting an engine speed, for example (stepS200). During the operation of the engine (NO in step S200), thepressure release control is unnecessary. Thus, the pressure releasecontrol routine is terminated, without performing the pressure releasefrom the low-pressure fuel supply system (low-pressure delivery pipe160) or from the high-pressure fuel supply system (high-pressuredelivery pipe 130).

On the other hand, at the stop of the engine (YES in step S200), theoperation of low-pressure fuel pump 180 is stopped (step S210). Thisdecreases the fuel pressure of the low-pressure fuel supply systemincluding low-pressure delivery pipe 160, as described in conjunctionwith FIG. 2.

At the stop of the engine, engine ECU 300 further determines whether theoperation of the vehicle is being continued, to distinguish thetemporary stop of the engine by the engine intermittent operationcontrol from the stop of the engine associated with the end of vehicleoperation (step S220).

For example, if the ignition key is not turned off, it is determinedthat it is the temporary stop of the engine with the vehicle operationbeing continued. During the temporary stop of the engine (YES in stepS220), actuation (opening) of electromagnetic relief valve 210 is notallowed (or, is prohibited) (step S230) so as to quickly secure the fuelpressure required for restart of the engine.

On the other hand, if the ignition key is off, it is recognized to bethe stop of the engine associated with the end of vehicle operation. Atthe stop of the engine associated with the end of vehicle operation (NOin step S220), actuation of electromagnetic relief valve 210 is allowed(step S240) so as not to cause deterioration in emission performance atthe time of next start of the engine due to leakage of the fuel becauseof degradation in oil tightness of injectors 110, 120 during the vehicleoperation stop period. At the stop of the engine associated with the endof vehicle operation, if another prescribed condition is furthersatisfied, the fuel pressure in the high-pressure fuel supply systemincluding high-pressure delivery pip 130 is decreased by actuation ofelectromagnetic relief valve 210. This permits release of the fuelpressure from both of the low-pressure fuel supply system and thehigh-pressure fuel supply system, so that degradation of oil tightnessduring the vehicle operation stop period can be prevented.

With the pressure release control as in FIG. 4, the operations ofelectromagnetic relief valve 210 and low-pressure fuel pump 180 of theinternal combustion engine according to the embodiment of the presentinvention are controlled as shown in FIG. 5.

Referring to FIG. 5, at the start of vehicle operation corresponding toturning on of the ignition key, electromagnetic relief valve 210 ischanged from the open state to the closed state. Further, operation oflow-pressure fuel pump 180 is started, and the fuel pressure in thelow-pressure fuel supply system begins to increase toward a necessarylevel. At the start of vehicle operation, the timing of starting engine10 is set at the time point when the fuel pressure of a required levelis guaranteed in the low-pressure fuel supply system by operation oflow-pressure fuel pump 180.

At the temporary stop of the engine according to the engine intermittentoperation control (FIG. 3), operation of low-pressure fuel pump 180 isalso stopped. Stopping the operation of low-pressure fuel pump 180during the time period where fuel injection is unnecessary can improvefuel efficiency by reduction of consumed power. Meanwhile,electromagnetic relief valve 210 remains closed, of which actuation isnot allowed.

At the stop of the engine associated with the end of vehicle operationcorresponding to turning off of the ignition key, operation oflow-pressure fuel pump 180 is stopped, and electromagnetic relief valve210 is actuated and opened as well. Consequently, the fuel pressure inthe low-pressure fuel system (particularly, low-pressure delivery pipe160) as well as in the high-pressure fuel supply system (particularly,high-pressure delivery pipe 130) decreases, and thus, degradation of oiltightness during the vehicle operation stop period is prevented.

Immediately after the end of vehicle operation, the temperature of thefuel in high-pressure delivery pipe 130 is likely to be high. Ifelectromagnetic relief valve 210 is opened in this state to rapidlydecrease the pressure, vapor lock may occur in the fuel supply systemdue to boiling under reduced pressure.

Thus, as shown in FIG. 6, the timing for actuating (opening)electromagnetic relief valve 210 at the time of engine stop associatedwith the end of vehicle operation may be set at a time point apredetermined time Tp after the end of vehicle operation. Thepredetermined time Tp is set to guarantee a period of time during whichthe temperature of the fuel in high-pressure delivery pipe 130 isdecreased to the level that can prevent such boiling under reducedpressure.

In the configuration of the fuel supply system shown in FIG. 2,low-pressure delivery pipe 160 is arranged upstream of fuel pressureregulator 170. Thus, it is difficult to secure a fuel pressure of arequired level in low-pressure delivery pipe 160 at the time of restartfollowing temporary stop of the engine, hindering normal fuel injectionfrom intake manifold injectors 120 upon the engine restart. Meanwhile,electromagnetic relief valve 210 is maintained in the closed state evenduring the temporary stop of the engine, and therefore, the fuelpressure in high-pressure delivery pipe 130 for delivering the fuel intoin-cylinder injectors 110 is maintained at a required level. Thus, fuelinjection using in-cylinder injectors 110 can be performed normally evenat the restart of the engine.

Taking into consideration the above-described points, in the internalcombustion engine according to the embodiment of the present invention,the engine startup-time control as shown in FIG. 7 is carried out.

Referring to FIG. 7, at the start of the engine, engine ECU 300determines whether the relevant engine start is the one associated withstart of vehicle operation. If it is not the engine start associatedwith start of vehicle operation, i.e., if it is not the initial enginestart following turning on of the ignition key, then it is determined tobe restart of the engine by the engine intermittent operation control.As described above, at the restart of the engine, while it is difficultto quickly increase the fuel pressure in low-pressure delivery pipe 160because low-pressure fuel pump 180 is being stopped, the fuel pressurein high-pressure delivery pipe 130 is maintained at a certain levelbecause electromagnetic relief valve 210 is kept closed.

Thus, at the restart of the engine (NO in step S300), engine ECU 300sets the DI ratio r near 100% (step S310) such that the fuel of almostall of the total fuel injection quantity required is injected viain-cylinder injector 110, and then starts cranking (step S350). Herein,the DI ratio r refers to a ratio of the quantity of the fuel injectedfrom in-cylinder injector 110 to a total quantity of the fuel injectedfrom both in-cylinder injector 110 and intake manifold injector 120.

Generally, in the cold state of the internal combustion engine,atomization of the fuel within the cylinder would not be promoted, andthe fuel injected from in-cylinder injector 110 tends to adhere to thetop face of the engine piston (piston top face) or the inner peripheralsurface of the cylinder (cylinder inner face (bore)) in a greatquantity. Of the fuel thus adhered, particularly the fuel adhered to thepiston top face will be gradually atomized during the subsequent enginecombustion process, and discharged from the cylinder in the state ofimperfect combustion. This will cause generation of black smoke,increase of unburned components and the like, leading to deteriorationin emission performance. Further, the fuel adhered to the cylinder innerface will be mixed with the lubricant applied to the cylinder inner facefor lubrication of the engine piston, thereby impairing the lubricationproperty of the internal combustion engine.

At the temporary stop as well as at the restart of engine 10 by theengine intermittent operation control shown in FIG. 3, however, thetemperature inside engine 10, or, in the combustion chamber, has beenincreased. Three-way catalytic converter 90 has also been increased intemperature and thus activated, so that there is only a smallpossibility that in-cylinder fuel injection would cause theabove-described adverse effect. Accordingly, in the fuel supply systemshown in FIG. 2, the restart of the engine by the engine intermittentoperation control is effected with the in-cylinder fuel injection,whereby quick starting capability is secured and deterioration inemission performance is also prevented.

In the case of engine start associated with start of vehicle operation(YES in step S300), the engine needs to be started in the engine coldstate. Thus, it is necessary to avoid the inconvenience of thein-cylinder fuel injection as described above. Accordingly, engine ECU300 sets DI ratio r near 0% (i.e., PFI (Port Fuel Injection) ratio near100%) (step S320) such that the fuel of almost all of the total fuelinjection quantity required is to be injected from intake manifoldinjector 120, and starts cranking (step S350). In this manner, it ispossible to prevent deterioration in emission performance at the time ofengine start associated with start of vehicle operation.

Step S310 in the flowchart of FIG. 7 corresponds to the “firststartup-time injection control means” and step S320 corresponds to the“second startup-time injection control means” of the present invention.Further, the functional part of engine ECU 300 controlling the DI ratiocorresponds to the “fuel injection control means” of the presentinvention.

Hereinafter, preferable engine startup-time control when the enginesystem shown in FIGS. 1 and 2 is incorporated into a hybrid vehicle willbe described.

Firstly, a schematic configuration of a hybrid vehicle will be explainedwith reference to FIG. 8.

Referring to FIG. 8, the hybrid vehicle 500 includes, in addition to anengine 540, a battery 510, a power control unit (PCU) 520 for convertingpower, an electric motor 530, a power split mechanism 550, a powergenerator (generator) 560, a reduction gear 570, driving wheels 580 a,580 b, and a hybrid ECU 590 that controls an overall operation of hybridvehicle 500.

Although a hybrid vehicle of which only the front wheels are the drivingwheels is shown in FIG. 8, another electric motor for driving the rearwheels may be provided to implement a 4-WD hybrid vehicle.

Battery 510 is configured with a rechargeable secondary battery (ofnickel hydrogen or lithium ion, for example). PCU 520 includes aninverter (not shown) for converting a direct-current (DC) voltagesupplied from battery 510 to an alternating-current (AC) voltage fordriving electric motor 530. The inverter is configured to perform powerconversion in both directions, and also has a function of converting thepower (AC voltage) generated by the regenerative braking operation ofelectric motor 530 as well as the power (AC voltage) generated bygenerator 560 to a DC voltage for charging battery 510.

Further, PCU 520 may also include a step up-and-down converter (notshown) to perform level conversion of the DC voltage. Provision of sucha step up-and-down converter makes it possible to drive electric motor530 by an AC voltage having the amplitude of higher voltage than thesupply voltage of battery 510, which can improve motor drivingefficiency.

As engine 540, the engine system shown in FIG. 1, for example, isapplied. Power split mechanism 550 can split the driving force generatedby the engine into two parts and deliver them to the path fortransmission to driving wheels 580 a, 580 b via reduction gear 570, andto the path for transmission to generator 560. Generator 560 is rotatedby the driving force from engine 540 transmitted via power splitmechanism 550, to generate power. The electric power generated bygenerator 560 is used by PCU 520, as the charging power of battery 510,or as the driving power of electric motor 530.

Electric motor 530 is rotated and driven by the AC voltage supplied fromPCU 520. The driving force of electric motor 530 is transmitted viareduction gear 570 to driving wheels 580 a, 580 b, to serve as thevehicle driving force. That is, electric motor 530 corresponds to the“other driving force source” in the present invention. In theregenerative braking operation in which electric motor 530 is rotatedwith reduction in speed of driving wheels 580 a, 580 b, electric motor530 functions as a power generator.

The start of vehicle operation in the hybrid vehicle corresponds toactivation of the hybrid system, i.e., the state where battery 510identified as the power source for driving the wheels is connected toelectric motor 530 to enable running by electric motor 530. Meanwhile,the stop of vehicle operation in the hybrid vehicle corresponds to stopof the hybrid system, i.e., the state where battery 510 being thehigh-pressure power source for driving the wheels is disconnected fromelectric motor 530.

Hybrid vehicle 500, at the time of light load when starting moving ordriving at low speed or climbing a moderate slope, runs with the drivingforce of electric motor 530, rather than the driving force of engine540, to avoid the low-efficiency region of the engine. As such,operation of engine 540 is stopped unless warm-up operation isnecessary. When such warm-up operation is required, engine 540 isoperated at idle.

In the normal running, engine 540 is started, and the driving forceoutput from engine 540 is split by power split mechanism 550 into thedriving force of driving wheels 580 a, 580 b and the driving force forgenerating power in generator 560. The power generated by generator 560is used to drive electric motor 530. Thus, during the normal running,the driving force by electric motor 530 assists the driving force byengine 540 to drive driving wheels 580 a, 580 b. Hybrid ECU 590 controlsthe power splitting ratio by power split mechanism 550 such that theoverall efficiency becomes maximum. Further, at full acceleration, thepower supplied from battery 510 is further used for driving electricmotor 530, so that the force for driving the driving wheels 580 a, 580 bfurther increases.

Upon speed reduction and braking, electric motor 530 is rotated anddriven by driving wheels 580 a, 580 b, to generate power. The electricpower collected by regenerative power generation of electric motor 530is converted to a DC voltage by PCU 520, and used for charging battery510. At the time of stop of the vehicle, engine 540 is automaticallystopped.

As described above, hybrid vehicle 500 achieves vehicle operationimproved in fuel efficiency, by combination of the driving forcegenerated by engine 540 and the driving force generated by electricmotor 530 using electric energy as a source, that is, by controlling theoperations of engine 540 and electric motor 530 according to the stateof the vehicle. Specifically, hybrid ECU 590 controls the ratio of thedriving force generated by electric motor 530 and engine 540 inaccordance with the operation state.

Accordingly, in the hybrid vehicle, the driving force by engine 540 isnot immediately necessary at the time of start of vehicle operation.Thus, it is possible to carry out the engine startup-time control asdescribed below to quickly increase the fuel pressure in low-pressuredelivery pipe 160 and in high-pressure delivery pipe 130 for preparationof start of operation of the internal combustion engine.

Referring to FIG. 9, in the engine startup-time control of the hybridvehicle, engine ECU 300 determines whether the engine start correspondsto the one associated with start of vehicle operation or it correspondsto the engine restart by the engine intermittent operation control, byexecution of step S300 that is similar to step S300 in FIG. 7.

In the case of the engine start associated with start of vehicleoperation (YES in step S300), engine ECU 300 issues an activationinstruction of low-pressure fuel pump 180 (step S305), prior to issuanceof a starting instruction of engine 10.

Further, engine ECU 300 performs step S320 similar to that of FIG. 7, toset DI ratio r near 0% such that the engine start in the engine coldstate is carried out by fuel injection via intake manifold injector 120.

Further, in step S330, engine ECU 300 determines whether a fuel pressureof a required level is guaranteed in the low-pressure fuel supply systemby activation of low-pressure fuel pump 180 in step S305. If so (YES instep S330), cranking is started (step S350) at the DI ratio (r≈0%)having been set in step S320.

If a necessary fuel pressure is not secured in the low-pressure fuelsupply system (NO in step S330), cranking is awaited (step S360).Further, while cranking is being awaited, if the request of the vehicledriving force is increased by press-down of the accelerator pedal or thelike (YES in step S340), then hybrid ECU 590 sets an output torquecommand value such that the driving force generated by electric motor(motor) 530 increases corresponding to the increase of the requesteddriving force (step S345).

At the engine restart by the engine intermittent operation control, stepS310 similar to that of FIG. 7 is carried out to set DI ratio r near100% such that the fuel of almost all of the total fuel injectionquantity required is injected from in-cylinder injector 110, and thencranking is started (step S350).

In the hybrid vehicle, at the time of engine start in the engine coldstate associated with start of vehicle operation, an operationinstruction of low-pressure fuel pump 180 is issued prior to the enginestart. This allows fuel pressure of a required level for the fuelinjected from intake manifold injector 120 to be secured more quickly,so that smooth engine start is achieved. Further, during the time periodwhere engine start cannot be done with intake manifold injection due toan insufficient fuel pressure or the like, the driving force generatedby electric motor 530 can be employed to address the increase of thevehicle driving force requested by the driver, so that startingcapability of the vehicle can be guaranteed.

As described above, the fuel supply system shown in FIG. 2 is capable ofreleasing pressure in each of the high-pressure fuel system and thelow-pressure fuel system, and accordingly, it is possible to apply thepressure release control as well as the engine startup-time control ofthe embodiment of the present invention to secure smooth startingcapability and to prevent deterioration in emission performance.

(Other Configuration Example of Fuel Supply System)

Hereinafter, another configuration example of the fuel supply system forthe internal combustion engine according to the embodiment of thepresent invention will be described.

Referring to FIG. 10, the fuel supply system of the other configurationexample differs from the fuel supply system shown in FIG. 2 in that thefuel discharged from low-pressure fuel pump 180 and passed through fuelpressure regulator 170 is guided to branched paths of one directed tolow-pressure delivery pipe 160 and the other directed to high-pressuredelivery pipe 130.

The fuel discharged from low-pressure fuel pump 180 of the electricmotor-driven type is supplied via fuel filter 190 to fuel pressureregulator 170. Fuel pressure regulator 170 is arranged upstream oflow-pressure delivery pipe 160, and is configured to return a part ofthe fuel discharged from low-pressure fuel pump 180 back to fuel tank200 when the fuel pressure of the discharged fuel becomes greater than apreset fuel pressure. This ensures that the fuel pressure on thedownstream side of fuel pressure regulator 170 is maintained at thepreset fuel pressure or lower.

On the downstream side of fuel pressure regulator 170, branched fuelpipes 135 and 136 are provided. The fuel discharged from low-pressurefuel pump 180 and passed through fuel pressure regulator 170 isdelivered via fuel pipe 135 to low-pressure delivery pipe 160. Anelectromagnetic relief valve 205 is provided in a fuel path extendingfrom fuel pressure regulator 170 to low-pressure delivery pipe 160, at acertain position of fuel pipe 135.

When the fuel pressure in fuel pipe 135 becomes greater than aprescribed pressure, electromagnetic relief valve 205 forms a path forguiding a part of the fuel to fuel return pipe 220. It is actuated(opened) in response to a control signal from ECU 300# to form a pathextending from fuel pipe 135 to fuel return pipe 220 so as to lower thefuel pressure in low-pressure delivery pipe 160 and in fuel pipe 135.

Fuel pipe 136 is connected to the intake side of high-pressure fuel pump155. An electromagnetic spill valve 156 is provided on the dischargeside of high-pressure fuel pump 155. The discharge side of high-pressurefuel pump 155 is connected via fuel pipe 165 to high-pressure deliverypipe 130.

Further, on the downstream side of high-pressure delivery pipe 130, anelectromagnetic relief valve 210 is arranged between the pipe 130 andfuel return pipe 220, as in the configuration example of FIG. 2.

In the configuration of the fuel supply system shown in FIG. 10, thepressure of the low-pressure fuel supply system (particularly,low-pressure delivery pipe 160) cannot be released by stoppinglow-pressure fuel pump 180. Thus, electromagnetic relief valve 205serving as the pressure release means of the low-pressure fuel supplysystem is additionally provided.

In the fuel supply system shown in FIG. 10, electromagnetic relief valve205 corresponds to the “second pressure release means” of the presentinvention.

In the fuel supply system shown in FIG. 10, the pressure release controlsimilar to that in FIG. 4 is carried out, by making the timing ofactuation of electromagnetic relief valve 205 similar to that ofelectromagnetic relief valve 210. As a result, the operation of the fuelsupply system shown in FIG. 10 becomes as shown in FIG. 11.

Referring to FIG. 11, low-pressure fuel pump 180 is operated insynchronization with the operating period of engine 10, as in the caseshown in FIG. 5. That is, low-pressure fuel pump 180 is stopped whileengine 10 is temporarily stopped.

Electromagnetic relief valves 205 and 210 are controlled in the samemanner as electromagnetic relief valve 205 of FIG. 5, to be closed inresponse to start of vehicle operation and to be actuated (opened) inresponse to end of vehicle operation. That is, during the temporary stopperiod of engine 10, actuation of electromagnetic relief valves 205 and210 is prohibited and they are maintained in the closed state.

As such, in the fuel supply system shown in FIG. 10, at the time of stopof vehicle operation, the fuel pressure in high-pressure delivery pipe130 (high-pressure fuel supply system) is decreased by actuation(opening) of electromagnetic relief valve 210, and the fuel pressure inlow-pressure delivery pipe 160 (low-pressure fuel supply system)arranged downstream of fuel pressure regulator 170 is also decreasedsufficiently by actuation (opening) of electromagnetic relief valve 205.Accordingly, as in the case of the fuel injection system shown in FIG.2, it is possible to suppress leakage of the fuel attributable todegradation in oil tightness of in-cylinder injectors 110 and intakemanifold injectors 120 during the stop of vehicle operation, to therebyprevent deterioration in emission performance upon engine start at thenext start of vehicle operation.

The engine startup-time control in the vehicle provided with the enginesystem (internal combustion engine) having the fuel supply system shownin FIG. 10 can be carried out according to FIG. 7 or FIG. 9 (hybridvehicle). In the fuel injection system shown in FIG. 10, during thetemporary stop period of engine 10 by the engine intermittent operationcontrol, both of electromagnetic relief valves 205 and 210 remainclosed, which can maintain the required fuel pressure at both of thehigh-pressure fuel supply system (high-pressure delivery pipe 130) andthe low-pressure fuel supply system (low-pressure delivery pipe 160).Accordingly, at the time of engine restart, both of in-cylinder injector110 and intake manifold injector 120 are ready to inject the fuel.

Taking the above-described point into consideration, at the time ofsetting the DI ratio (step S3 10 in FIGS. 7 and 9) upon restart aftertemporary stop of the engine, the DI ratio can be set according to thetemperature of the engine, rather than being set near 100%. Morespecifically, when the temperature ofthe engine is low (in the enginecold state), the DI ratio may be set near 0% to inject the fuel ofalmost all of the total fuel injection quantity from intake manifoldinjector 120, so as to prevent adhesion of the fuel to the cylinder andthe piston. When the engine is sufficiently warm, the DI ratio may beset corresponding to the engine condition to allow fuel injection fromin-cylinder injector 110 as well, to quickly ensure required poweroutput. Altematively, the DI ratio of the intermediate range may be setdepending on the situations.

Further, as shown in FIG. 12, in the fuel supply system shown in FIG. 10as well, the timing of actuation (opening) of electromagnetic reliefvalves 205, 210 at the time of engine stop associated with end ofvehicle operation may be set at a time point a predetermined time Tpafter the end of vehicle operation, so as to prevent vapor lock thatwould occur when the pressure is rapidly lowered while the fueltemperature is still high.

As described above, in the fuel supply system of FIG. 10 as well, it ispossible to release the fuel pressure in both of the high-pressure fuelsystem and the low-pressure fuel system, so that smooth startingcapability can be secured and deterioration in emission performance canbe prevented by applying the pressure release control and the enginestartup-time control of the embodiment of the present invention.

(Preferable DI Ratio Setting in Normal Operation)

Hereinafter, a first example of preferable setting of a DI ratio in anormal operation of the internal combustion engine according to theembodiment of the present invention will be described.

Referring to FIGS. 13 and 14, maps each indicating a fuel injectionratio between in-cylinder injector 110 and intake manifold injector 120,identified as information associated with an operation state of engine10, will now be described. Herein, the fuel injection ratio between thetwo injectors is also expressed as a ratio of the quantity of the fuelinjected from in-cylinder injector 110 to the total quantity of the fuelinjected, which is referred to as the “fuel injection ratio ofin-cylinder injector 110”, or a “DI (Direct Injection) ratio (r)”. Themaps are stored in ROM 320 of engine ECU 300. FIG. 13 is the map for awarm state of engine 10, and FIG. 14 is the map for a cold state ofengine 10.

In the maps illustrated in FIGS. 13 and 14, with the horizontal axisrepresenting an engine speed of engine 10 and the vertical axisrepresenting a load factor, the fuel injection ratio of in-cylinderinjector 110, or the DI ratio r, is expressed in percentage.

As shown in FIGS. 13 and 14, the DI ratio r is set for each operationregion that is determine by the engine speed and the load factor ofengine 10. “DI RATIO r=100%” represents the region where fuel injectionis carried out using only in-cylinder injector 110, and “DI RATIO r=0%”represents the region where fuel injection is carried out using onlyintake manifold injector 120. “DI RATIO r≠0%”, “DI RATIO r≠100%” and“0%<DI RATIO r<100%” each represent the region where fuel injection iscarried out using both in-cylinder injector 110 and intake manifoldinjector 120. Generally, in-cylinder injector 110 contributes to anincrease of output performance, while intake manifold injector 120contributes to uniformity of the air-fuel mixture. These two kinds ofinjectors having different characteristics are appropriately selecteddepending on the engine speed and the load factor of engine 10, so thatonly homogeneous combustion is conducted in the normal operation stateof engine 10 (other than the abnormal operation state such as a catalystwarm-up state at idle).

Further, as shown in FIGS. 13 and 14, the fuel injection ratio betweenin-cylinder injector 110 and intake manifold injector 120, or, the DIratio r, is defined individually in the map for the warm state and inthe map for the cold state of the engine. The maps are configured toindicate different control regions of in-cylinder injector 110 andintake manifold injector 120 as the temperature of engine 10 changes.When the temperature of engine 10 detected is equal to or higher than apredetermined temperature threshold value, the map for the warm stateshown in FIG. 13 is selected; otherwise, the map for the cold stateshown in FIG. 14 is selected. One or both of in-cylinder injector 110and intake manifold injector 120 are controlled based on the selectedmap and according to the engine speed and the load factor of engine 10.

The engine speed and the load factor of engine 10 set in FIGS. 13 and 14will now be described. In FIG. 13, NE(1) is set to 2500 rpm to 2700 rpm,KL(1) is set to 30% to 50%, and KL(2) is set to 60% to 90%. In FIG. 14,NE(3) is set to 2900 rpm to 3100 rpm. That is, NE(1)<NE(3). NE(2) inFIG. 13 as well as KL(3) and KL(4) in FIG. 14 are also set asappropriate.

When comparing FIG. 13 and FIG. 14, NE(3) of the map for the cold stateshown in FIG. 14 is greater than NE(1) of the map for the warm stateshown in FIG. 13. This shows that, as the temperature of engine 10 islower, the control region of intake manifold injector 120 is expanded toinclude the region of higher engine speed. That is, in the case whereengine 10 is cold, deposits are unlikely to accumulate in the injectionhole of in-cylinder injector 110 (even if the fuel is not injected fromin-cylinder injector 110). Thus, the region where the fuel injection isto be carried out using intake manifold injector 120 can be expanded, tothereby improve homogeneity.

When comparing FIG. 13 and FIG. 14, “DI RATIO r=100%” holds in theregion where the engine speed of engine 10 is NE(1) or higher in the mapfor the warm state, and in the region where the engine speed is NE(3) orhigher in the map for the cold state. In terms of load factor, “DI RATIOr=100%” holds in the region where the load factor is KL(2) or greater inthe map for the warm state, and in the region where the load factor isKL(4) or greater in the map for the cold state. This means thatin-cylinder injector 110 alone is used in the region of a predeterminedhigh engine speed, as well as in the region of a predetermined highengine load. That is, in the high speed region or the high load region,even if fuel injection is carried out using only in-cylinder injector110, the engine speed and the load of engine IO are high, ensuring asufficient intake air quantity, so that it is readily possible to obtaina homogeneous air-fuel mixture using in-cylinder injector 110 alone. Inthis manner, the fuel injected from in-cylinder injector 110 is atomizedwithin the combustion chamber involving latent heat of vaporization (or,absorbing heat from the combustion chamber). Thus, the temperature ofthe air-fuel mixture is decreased at the compression end, wherebyantiknock performance is improved. Further, since the temperature withinthe combustion chamber is decreased, intake efficiency improves, leadingto high power output.

In the map for the warm state in FIG. 13, fuel injection is also carriedout using only in-cylinder injector 110 when the load factor is KL(1) orless. This shows that in-cylinder injector 110 alone is used in apredetermined low load region when the temperature of engine 10 is high.When engine 10 is in the warm state, deposits are likely to accumulatein the injection hole of in-cylinder injector 110. However, when fuelinjection is carried out using in-cylinder injector 110, the temperatureof the injection hole can be lowered, whereby accumulation of depositsis prevented. Further, clogging of in-cylinder injector 10 may beprevented while ensuring the minimum fuel injection quantity thereofThus, in-cylinder injector 10 alone is used in the relevant region.

When comparing FIG. 13 and FIG. 14, there is a region of “DI RATIO r=0%”only in the map for the cold state in FIG. 14. This shows that fuelinjection is carried out using only intake manifold injector 120 in apredetermined low load region (KL(3) or less) when the temperature ofengine 10 is low. When engine 10 is cold and low in load and the intakeair quantity is small, atomization of the fuel is unlikely to occur. Insuch a region, it is difficult to ensure favorable combustion with thefuel injection from in-cylinder injector 110. Further, particularly inthe low-load and low-speed region, high power output using in-cylinderinjector 110 is unnecessary. Accordingly, fuel injection is carried outusing intake manifold injector 120 alone, rather than using in-cylinderinjector 110, in the relevant region.

Further, in an operation other than the normal operation, i.e., in thecatalyst warm-up state at idle of engine 10 (abnormal operation state),in-cylinder injector 110 is controlled to carry out stratified chargecombustion. By causing the stratified charge combustion during thecatalyst warm-up operation, warming up of the catalyst is promoted, andexhaust emission is thus improved.

Hereinafter, a second example of the DI ratio in the normal operation ofthe internal combustion engine according to the embodiment of thepresent invention will be described.

Referring to FIGS. 15 and 16, maps each indicating the fuel injectionratio between in-cylinder injector 110 and intake manifold injector 120,identified as information associated with the operation state of engine10, will be described. The maps are stored in ROM 320 of engine ECU 300.FIG. 15 is the map for the warm state of engine 10, and FIG. 16 is themap for the cold state of engine 10.

FIGS. 15 and 16 differ from FIGS. 13 and 14 in the following points. “DIRATIO r=100%” holds in the region where the engine speed of engine 10 isequal to or higher than NE(1) in the map for the warm state, and in theregion where the engine speed is NE(3) or higher in the map for the coldstate. Further, except for the low-speed region, “DI RATIO r=100%” holdsin the region where the load factor is KL(2) or greater in the map forthe warm state, and in the region where the load factor is KL(4) orgreater in the map for the cold state. This means that fuel injection iscarried out using only in-cylinder injector 110 in the region where theengine speed is at a predetermined high level, and that fuel injectionis often carried out using only in-cylinder injector 110 in the regionwhere the engine load is at a predetermined high level. However, in thelow-speed and high-load region, mixing of an air-fuel mixture formed bythe fuel injected from in-cylinder injector 110 is poor, and suchinhomogeneous air-fuel mixture within the combustion chamber may lead tounstable combustion. Thus, the fuel injection ratio of in-cylinderinjector 110 is increased as the engine speed increases where such aproblem is unlikely to occur, whereas the fuel injection ratio ofin-cylinder injector 110 is decreased as the engine load increases wheresuch a problem is likely to occur. These changes in the fuel injectionratio of in-cylinder injector 110, or, the DI ratio r, are shown bycrisscross arrows in FIGS. 15 and 16. In this manner, variation inoutput torque of the engine attributable to the unstable combustion canbe suppressed. It is noted that these measures are approximatelyequivalent to the measures to decrease the fuel injection ratio ofin-cylinder injector 110 as the state of the engine moves toward thepredetermined low speed region, or to increase the fuel injection ratioof in-cylinder injector 110 as the engine state moves toward thepredetermined low load region. Further, except for the relevant region(indicated by the crisscross arrows in FIGS. 15 and 16), in the regionwhere fuel injection is carried out using only in-cylinder injector 110(on the high speed side and on the low load side), a homogeneousair-fuel mixture is readily obtained even when the fuel injection iscarried out using only in-cylinder injector 110. In this case, the fuelinjected from in-cylinder injector 110 is atomized within the combustionchamber involving latent heat of vaporization (by absorbing heat fromthe combustion chamber). Accordingly, the temperature of the air-fuelmixture is decreased at the compression side, and thus, the antiknockperformance improves. Further, with the temperature of the combustionchamber decreased, intake efficiency improves, leading to high poweroutput.

In this engine 10 explained in conjunction with FIGS. 13-16, homogeneouscombustion is achieved by setting the fuel injection timing ofin-cylinder injector 110 in the intake stroke, while stratified chargecombustion is realized by setting it in the compression stroke. That is,when the fuel injection timing of in-cylinder injector 110 is set in thecompression stroke, a rich air-fuel mixture can be established locallyaround the spark plug, so that a lean air-fuel mixture in the combustionchamber as a whole is ignited to realize the stratified chargecombustion. Even if the fuel injection timing of in-cylinder injector110 is set in the intake stroke, stratified charge combustion can berealized if it is possible to provide a rich air-fuel mixture locallyaround the spark plug.

As used herein, the stratified charge combustion includes both thestratified charge combustion and semi-stratified charge combustion. Inthe semi-stratified charge combustion, intake manifold injector 120injects fuel in the intake stroke to generate a lean and homogeneousair-fuel mixture in the whole combustion chamber, and then in-cylinderinjector 110 injects fuel in the compression stroke to generate a richair-fuel mixture locally around the spark plug, so as to improve thecombustion state. Such semi-stratified charge combustion is preferablein the catalyst warm-up operation for the following reasons. In thecatalyst warm-up operation, it is necessary to considerably retard theignition timing and maintain a favorable combustion state (idle state)so as to cause a high-temperature combustion gas to reach the catalyst.Further, a certain quantity of fuel needs to be supplied. If thestratified charge combustion is employed to satisfy these requirements,the quantity of the fuel will be insufficient. If the homogeneouscombustion is employed, the retarded amount for the purpose ofmaintaining favorable combustion is small compared to the case ofstratified charge combustion. For these reasons, the above-describedsemi-stratified charge combustion is preferably employed in the catalystwarm-up operation, although either of stratified charge combustion andsemi-stratified charge combustion may be employed.

Further, in the engine explained in conjunction with FIGS. 13-16, thefuel injection timing of in-cylinder injector 110 is set in the intakestroke in a basic region corresponding to the almost entire region(here, the basic region refers to the region other than the region wheresemi-stratified charge combustion is carried out with fuel injectionfrom intake manifold injector 120 in the intake stroke and fuelinjection from in-cylinder injector 110 in the compression stroke, whichis carried out only in the catalyst warm-up state). The fuel injectiontiming of in-cylinder injector 110, however, may be set temporarily inthe compression stroke for the purpose of stabilizing combustion, forthe following reasons.

When the fuel injection timing of in-cylinder injector 110 is set in thecompression stroke, the air-fuel mixture is cooled by the injected fuelwhile the temperature in the cylinder is relatively high. This improvesthe cooling effect and, hence, the antiknock performance. Further, whenthe fuel injection timing of in-cylinder injector 110 is set in thecompression stroke, the time from the fuel injection to the ignition isshort, which ensures strong penetration of the injected fuel, so thatthe combustion rate increases. The improvement in antiknock performanceand the increase in combustion rate can prevent variation in combustion,and thus, combustion stability is improved.

Further, in the off-idle state (when the idle switch is off, and theaccelerator pedal is being pressed down), the DI ratio map for the warmstate as shown in FIG. 13 or 15 may be used (i.e., in-cylinder injector110 may be used) irrelevant to the temperature of engine 10 (i.e., inboth the warm state and the cold state of engine 1 0).

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A control apparatus for a vehicle incorporating an internalcombustion engine having a first fuel supply system supplying fuel tofirst fuel injection means for injecting fuel into a cylinder and asecond fuel supply system supplying fuel to second fuel injection meansfor injecting fuel into an intake manifold, comprising: fuel injectioncontrol means for controlling a fuel injection ratio between said firstfuel injection means and said second fuel injection means with respectto a total fuel injection quantity; intermittent operation control meansfor automatically stopping said internal combustion engine temporarilywhen a prescribed condition is satisfied after start of operation ofsaid vehicle; and first pressure release control means for controllingfirst pressure release means that is configured to guide the fuel insaid first fuel supply system to a pressure release path when actuated;wherein said first pressure release control means prohibits actuation ofsaid first pressure release means when said internal combustion engineis in an automatically stopped state by said intermittent operationcontrol means, and said fuel injection control means includes firststartup-time injection control means for setting a ratio of a quantityof the fuel injected from said first fuel injection means to the totalfuel injection quantity near 100% when said internal combustion engineis restarted from said automatically stopped state.
 2. The controlapparatus for a vehicle according to claim 1, further comprising secondpressure release control means for controlling second pressure releasemeans that is configured to release a fuel pressure of said second fuelsupply system when actuated, wherein said first and second pressurerelease control means actuate said first and second pressure releasemeans, respectively, in response to stop of said internal combustionengine in association with end of operation of said vehicle.
 3. Thecontrol apparatus for a vehicle according to claim 2, wherein said firstpressure release control means actuates said first pressure releasemeans at the end of operation of said vehicle, after a lapse of aprescribed time that is set to allow a decrease of a temperature of thefuel in said first fuel supply system to a prescribed level.
 4. Thecontrol apparatus for a vehicle according to claim 1, further comprisingfuel pump control means for controlling a fuel pump for securing a fuelpressure necessary for said second fuel supply system, wherein said fuelpump control means stops operation of said fuel pump each time when saidinternal combustion engine is automatically stopped by said intermittentoperation control means and when said internal combustion engine isstopped in association with end of operation of said vehicle.
 5. Thecontrol apparatus for a vehicle according to claim 1, wherein said fuelinjection control means includes second startup-time injection controlmeans for setting a ratio of a quantity of the fuel injected from saidsecond fuel injection means to the total fuel injection quantity near100% when said internal combustion engine is started in association withstart of operation of said vehicle.
 6. The control apparatus for avehicle according to claim 5, wherein said vehicle further incorporatesa driving force source besides said internal combustion engine, saidcontrol apparatus further comprising driving force ratio control meansfor controlling a ratio of driving force generated by said internalcombustion engine and by said driving force source in accordance with anoperation state, wherein said driving force ratio control means includesmeans for instructing said driving force source to generate drivingforce corresponding to the driving force required for said vehicle as awhole, when said internal combustion engine is started in associationwith start of operation of said vehicle, and when a fuel pressure insaid second fuel supply system is lower than a required level.
 7. Acontrol apparatus for a vehicle incorporating an internal combustionengine, having a first fuel supply system supplying fuel to first fuelinjection means for injecting fuel into a cylinder and a second fuelsupply system supplying fuel to second fuel injection means forinjecting fuel into an intake manifold, and a driving force source otherthan said internal combustion engine, comprising: driving force ratiocontrol means for controlling a ratio of driving force generated by saidinternal combustion engine and by said driving force source inaccordance with an operation state; and fuel injection control means forcontrolling a fuel injection ratio between said first fuel injectionmeans and said second fuel injection means with respect to a total fuelinjection quantity in said internal combustion engine; wherein said fuelinjection control means includes startup-time injection control meansfor setting a ratio of a quantity of the fuel injected from said secondfuel injection means to the total fuel injection quantity near 100% whensaid internal combustion engine is started in association with start ofoperation of said vehicle, and said driving force ratio control meansincludes means for instructing said driving force source to generatedriving force corresponding to the driving force required for saidvehicle as a whole, when a fuel pressure in said second fuel supplysystem is lower than a required level.
 8. The control apparatus for avehicle according to claim 7, further comprising fuel pump control meansfor controlling a fuel pump for securing a fuel pressure necessary forsaid second fuel supply system, wherein said fuel pump control meansincludes means for starting operation of said fuel pump before a startinstruction of said internal combustion engine is generated.
 9. Thecontrol apparatus for a vehicle according to claim 7, wherein saiddriving force source is an electric motor powered by a secondarybattery, and said vehicle further includes charge control means forcharging said secondary battery by power generated by regenerativebraking of said electric power and by power generated by driving forceof said internal combustion engine.
 10. A control apparatus for avehicle incorporating an internal combustion engine having a first fuelsupply system supplying fuel to a first fuel injection mechanism forinjecting fuel into a cylinder and a second fuel supply system supplyingfuel to a second fuel injection mechanism for injecting fuel into anintake manifold, comprising: a fuel injection control portion configuredto control a fuel injection ratio between said first fuel injectionmechanism and said second fuel injection mechanism with respect to atotal fuel injection quantity; an intermittent operation control portionconfigured to automatically stop said internal combustion enginetemporarily when a prescribed condition is satisfied after start ofoperation of said vehicle; and a first pressure release control portionconfigured to control a first pressure release mechanism that isconfigured to guide the fuel in said first fuel supply system to apressure release path when actuated; wherein said first pressure releasecontrol portion prohibits actuation of said first pressure releasemechanism when said internal combustion engine is in an automaticallystopped state by said intermittent operation control portion, and saidfuel injection control portion includes a first startup-time injectioncontrol portion configured to set a ratio of a quantity of the fuelinjected from said first fuel injection mechanism to the total fuelinjection quantity near 100% when said internal combustion engine isrestarted from said automatically stopped state.
 11. The controlapparatus for a vehicle according to claim 10, further comprising asecond pressure release control portion configured to control a secondpressure release mechanism that is configured to release a fuel pressureof said second fuel supply system when actuated, wherein said first andsecond pressure release control portions actuate said first and secondpressure release mechanisms, respectively, in response to stop of saidinternal combustion engine in association with end of operation of saidvehicle.
 12. The control apparatus for a vehicle according to claim 11,wherein said first pressure release control portion actuates said firstpressure release mechanism at the end of operation of said vehicle,after a lapse of a prescribed time that is set to allow a decrease of atemperature of the fuel in said first fuel supply system to a prescribedlevel.
 13. The control apparatus for a vehicle according to claim 10,further comprising a fuel pump control portion configured to control afuel pump for securing a fuel pressure necessary for said second fuelsupply system, wherein said fuel pump control portion stops operation ofsaid fuel pump each time when said internal combustion engine isautomatically stopped by said intermittent operation control portion andwhen said internal combustion engine is stopped in association with endof operation of said vehicle.
 14. The control apparatus for a vehicleaccording to claim 10, wherein said fuel injection control portionincludes a second startup-time injection control portion configured toset a ratio of a quantity of the fuel injected from said second fuelinjection mechanism to the total fuel injection quantity near 100% whensaid internal combustion engine is started in association with start ofoperation of said vehicle.
 15. The control apparatus for a vehicleaccording to claim 14, wherein said vehicle further incorporates adriving force source besides said internal combustion engine, saidcontrol apparatus further comprising a driving force ratio controlportion configured to control a ratio of driving force generated by saidinternal combustion engine and by said driving force source inaccordance with an operation state, wherein said driving force ratiocontrol portion instructs said driving force source to generate drivingforce corresponding to the driving force required for said vehicle as awhole, when said internal combustion engine is started in associationwith start of operation of said vehicle, and when a fuel pressure insaid second fuel supply system is lower than a required level.
 16. Acontrol apparatus for a vehicle incorporating an internal combustionengine, having a first fuel supply system supplying fuel to a first fuelinjection mechanism for injecting fuel into a cylinder and a second fuelsupply system supplying fuel to a second fuel injection mechanism forinjecting fuel into an intake manifold, and a driving force source otherthan said internal combustion engine, comprising: a driving force ratiocontrol portion configured to control a ratio of driving force generatedby said internal combustion engine and by said driving force source inaccordance with an operation state; and a fuel injection control portionconfigured to control a fuel injection ratio between said first fuelinjection mechanism and said second fuel injection mechanism withrespect to a total fuel injection quantity in said internal combustionengine; wherein said fuel injection control portion includes astartup-time injection control portion configured to set a ratio of aquantity of the fuel injected from said second fuel injection mechanismto the total fuel injection quantity near 100% when said internalcombustion engine is started in association with start of operation ofsaid vehicle, and said driving force ratio control portion instructssaid driving force source to generate driving force corresponding to thedriving force required for said vehicle as a whole, when a fuel pressurein said second fuel supply system is lower than a required level. 17.The control apparatus for a vehicle according to claim 16, furthercomprising a fuel pump control portion configured to control a fuel pumpfor securing a fuel pressure necessary for said second fuel supplysystem, wherein said fuel pump control portion starts operation of saidfuel pump before a start instruction of said internal combustion engineis generated.
 18. The control apparatus for a vehicle according to claim16, wherein said driving force source is an electric motor powered by asecondary battery, and said vehicle further includes a charge controlportion configured to charge said secondary battery by power generatedby regenerative braking of said electric motor and by power generated bydriving force of said internal combustion engine.